I've been taking fat burners for a few weeks, the caffine in them is about 100mg and i take 2, its about 4 cups of coffee (which i don't drink) i take them in the morning and i've had no trouble sleeping. They also have suppressed my appitite but not killed it, been having 3 meals a day and not felt the need to snack and i'm a grazer so its brilliant. I admit they're not for everyone, but if you get any major side effects stop taking them. Edphrdrine is banned in a lot of countries due to the links with heart problems, most don't have it in but its worth checking. I've googled them and there are some good and bad stories with most things, i'm not worried about heart problems mainly because at 22 stone i'm likely to get them if i don't lose weight. Just be sensible!